Field of the Invention
The present invention relates to an image forming apparatus for forming images onto papers. More particularly, the present invention provides the image forming apparatus and method that allow any deviation of the paper that may occur in the direction across the paper transporting direction to be compensated in preparation to the images forming.
Description of the Prior Art
In the image forming apparatus of the electronic photocopying type such as a copying machine, a printer machine, a facsimile machine, and a multi function machine that provides the functions of the aforementioned machines, an image forming unit is provided, in which a latent image corresponding to the image on the original document is formed onto the photosensitive element, this latent image is developed into an developed image by applying a toner onto the latent image, and the resulting toner image is finally transferred onto the paper. Following this, the toner image on the paper is fixed in the fixing unit and is outputted from the machine.
The papers mentioned above are usually placed on the paper feeding tray. When an image is to be formed, the papers on the tray are fed by the paper transporting unit to the image forming unit. For the paper having the image formed on the front side thereof, it is reversed to the rear side as required and then transported by the reversing and transporting unit. The reversed paper is then transported back to the paper transporting unit where the image is formed on the rear side of the paper.
When papers are to be supplied on the paper feeding tray, the paper guide plate may not be held firmly in the direction across the paper transporting direction or the paper guide plate itself may have the mechanical problem in that it is loosened permanently. If the papers are not held securely on the tray as described above, those papers may be incorrectly aligned in the direction across the paper transporting direction and then a deviation may occur when they are to be fed from the tray in the apparatus. This deviation may also occur due to the vibrations or the poor quality of any associated parts caused by the aging while the papers are being transported.
It may be apparent from the above description that the deviation can be compensated by the front side resist unit, and there are the two main types of the deviation, that is, the one that may be caused when the papers are to be fed and the one that may be caused while the papers are being transported.
For the deviation described above, the deviation compensating mechanism is proposed, in which such deviation can be compensated by shifting the paper being transported toward the direction across the paper transporting direction (ref. Patent Document 1, for example). In the deviation compensating mechanism proposed by Patent Document 1, the deviation compensating unit is allowed to be waiting on the point different from the original point before the deviation compensation, and it can then compensate the deviation. The restriction on the quantity by which the paper is to be shifted is reduced accordingly.
In the patent Document 2, the deviation is allowed to be compensated precisely by deciding the position of the output image in accordance with the deviation compensation of the paper.
In the patent Document 3, the invention related to the deviation compensation that allows the deviation to be compensated precisely is disclosed.
In the patent Document 4, the deviation of the paper across the width thereof is allowed to be compensated by shifting the deviated paper across the width thereof, wherein when the large-size papers are fluctuated, the load upon the driving motor will be increased, and so the paper feeding will be stopped in the paper fluctuating position where the paper will be shifted across the width thereof and will then be transported again.
The following is a list of the prior Patent Documents associated with the present invention:
Patent Document 1: Patent application laid open No. 2010-215374
Patent Document 2: Patent application laid open No. 2008-32913
Patent Document 3: Patent application laid open No. 2003-081489
Patent Document 4: Patent application laid open No. Heise3-094275